1. Field of the Invention
This invention relates to a silver halide photographic material having improved antiblocking property and film brittleness.
2. Description of the Prior Art
It is known that when a silver halide photographic material is stored at a high temperature and high humidity, in general, blocking trouble tends to occur between the surface of the light-sensitive material and the back surface. In order to prevent the blocking trouble, matting (roughening) of the surface has widely been carried out by incorporating organic or inorganic fine grains (so-called matting agent) in an emulsion layer of a photographic material or a surface-protective layer on a backing surface. The matting agent can have various sizes depending on the purpose thereof, but one having a range of 10 to 10 .mu.m in size is preferably used.
Since the matting agent generally contains a number of large sized grains exceeding 1 .mu.m, however, light-scattering is so much that in the case of color photographic materials, in particular, deterioration of the surface lustre, haze and graininess is caused and the amount of the matting agent to be used is thus limited.
Accordingly, another antiblocking technique has hitherto been known comprising adding colloidal silica or polymer latex each having a smaller grain size (i.e. submicron grain diameter) than the matting agent to a protective layer or emulsion layer jointly with the matting agent, as disclosed in, for example, Japanese Patent Laid-Open Publication No. 100226/1978 in which colloidal silica is added to a protective layer. In this case, however, there arises a problem that the film brittleness is worsened.
As a technique of adding a polymer latex, there are proposed further patents, for example, EP 751,422 in which a polymer latex having a glass transition temperature of at least 70.degree. C. is added to a protective layer and Japanese Patent Laid-Open Publication No. 251844/1986, in which a polymer latex having a glass transition temperature of at least 20.degree. C. and another polymer latex having a glass transition temperature of lower than 20.degree. C. are jointly used. According to these techniques, however, improvement of the film brittleness is not sufficient and the haze, surface lustre, etc. are somewhat deteriorated.
Many of the problems resulting from adding the fine grains are due to lacking in the affinity of the grain surfaces and hydrophilic colloid layer and the effect of the polymer latexes described in these two patents is not sufficient in spite of that a monomer having a hydrophilic functional group such as carboxylic group is incorporated in the polymer latex so as to increase the affinity with the hydrophilic colloid layer.
Japanese Patent Laid-Open Publication No. 134336/1993 discloses a technique comprising adding a polymer latex having a very large content, i.e. 5 to 100 mol % of carboxylic groups to a protective layer, but in this case, there arises a problem that the polymer latex tends to be dissolved in a processing solution due to be rendered excessively hydrophilic. When the grain diameter is further rendered smaller to improve the image quality, the grain surface area is too large to solve the problem of the dissolution.
Japanese Patent Laid-Open Publication No. 201950/1996 discloses a technique comprising adding a polymer latex having hydrophilic groups and being bridged to a protective layer, whereby dissolution in a processing solution can be prevented. However, the polymer latexes described therein are all soft (exhibiting a glass transition temperature of at most about 40.degree. C.) or rendering hydrophilic is insufficient so that improvement of the antiblocking effect is not achieved and the image quality is not good.
Japanese Patent Laid-Open Publication No. 138572/1994 also discloses a technique comprising adding a polymer latex having hydrophilic groups and being bridged to a protective layer, but this technical content is limited to a matting agent having a grain diameter of at least 2 .mu.m, thus raising a problem on deterioration of the image quality such as graininess.